The following publications are representative of the most relevant prior art known to Applicants at the time of filing of the Application.
______________________________________ UNITED STATES PATENTS ______________________________________ 3,937,792 February 10, 1976 R. J. Lumby 4,127,630 November 28, 1978 M. E. Washburn 4,869,943 September 26, 1989 N. D. Corbin et al. ______________________________________